Electrical submersible pumps (ESP) are commonly used in oil wells for pumping oil and formation water to the surface. An ESP comprises a pump having a downhole electrical motor. The pump typically is a centrifugal pump having a large number of stages, each stage having an impeller and a diffuser. Alternately, the pump could be another type, such as a progressing cavity pump. The ESP may also have one or more sensors for sensing well parameters such as pressure and temperature.
Normally the ESP is lowered into the well on production tubing which comprises joints approximately 30 feet in length secured together by threads. Alternately, the tubing could comprise continuous coiled tubing. A power cable is connected to the motor of the pump while it is at the surface and deployed from a reel while lowering into the well.
The ESP and power cable are subject to being damaged during running. Damage can result due to striking objects in the well, vibration, shock or from the well temperature. If the problem is discovered only after the ESP is completely installed, expense and time are incurred to pull the ESP, tubing and power cable from the well. The well could be thousands of feet deep. Consequently, it is not uncommon for the operator to stop the rig and connect the ends of the power cable to equipment on the surface to check the integrity of the system. Stopping the rig to perform these test adds to the running time for the ESP.
Downhole completion equipment other than ESPs also encounter the same problem. For example, sliding sleeve subs, packers, gravel packing tools, sand control screens and the like may include electrical actuators and/or sensors such as position indicating devices. These types of completion equipment are also run on tubing and may have an electrical line deployed from a reel.